In a dynamic rigid disk storage device, a rotating disk is employed to store information. Rigid disk storage devices typically include a frame to provide attachment points and orientation for other components, and a spindle motor mounted to the frame for rotating the disk. A read/write head is formed on a “head slider” for writing and reading data to and from the disk surface. The head slider is supported and properly oriented in relationship to the disk by a head suspension that provides both the force and compliance necessary for proper head slider operation. As the disk in the storage device rotates beneath the head slider and head suspension, the air above the disk also rotates, thus creating an air bearing which acts with an aerodynamic design of the head slider to create a lift force on the head slider. The lift force is counteracted by a spring force of the head suspension, thus positioning the head slider at a desired height and alignment above the disk which is referred to as the “fly height.”
Head suspensions for rigid disk drives include a load beam and a flexure. The load beam typically includes a mounting region at its proximal end for mounting the head suspension to an actuator of the disk drive, a rigid region, and a spring region between the mounting region and the rigid region for providing a spring force to counteract the aerodynamic lift force generated on the head slider during the drive operation as described above. The flexure typically includes a gimbal region having a slider mounting surface where the head slider is mounted. The gimbal region is resiliently moveable with respect to the remainder of the flexure in response to the aerodynamic forces generated by the air bearing. The gimbal region permits the head slider to move in pitch and roll directions and to follow disk surface fluctuations.
In one type of head suspension the flexure is formed as a separate piece having a load beam mounting region which is rigidly mounted to the distal end of the load beam using conventional methods such as spot welds. Head suspensions of this type typically include a load point dimple formed in either the load beam or the gimbal region of the flexure. The load point dimple transfers portions of the load generated by the spring region of the load beam, or gram load, to the flexure, provides clearance between the flexure and the load beam, and functions as a point about which the head slider can gimbal in pitch and roll directions to follow fluctuations in the disk surface.
Disk drive manufacturers continue to develop smaller yet higher storage capacity drives. Storage capacity increases are achieved in part by increasing the density of the information tracks on the disks (i.e., by using narrower and/or more closely spaced tracks). As track density increases, however, it becomes increasingly difficult for the motor and servo control system to quickly and accurately position the read/write head over the desired track. Attempts to improve this situation have included the provision of a another or secondary actuator or actuators, such as a piezoelectric, electrostatic or electromagnetic microactuator or fine tracking motor, mounted on the head suspension itself. These types of actuators are also known as second-stage microactuation devices and may be located at the base plate, the load beam or on the flexure.
Some of these attempts to improve tracking and head slider positioning control have included locating the microactuator at the head slider itself. Typically, this type of microactuator is sandwiched between the head slider and the head slider mounting surface of the flexure or other suspension component, or is otherwise directly coupled to the head slider. Movement of the microactuator then generally results in relatively direct movement of the head slider to provide the desired fine motion of the read/write head over the tracks of the disk drive.
One problem with this type of set up results from the need for the microactuator to produce enough force to overcome its own internal stiffness so that the desired amount of displacement is generated at the read/write head of the slider. The amount of force needed to generate a given displacement depends entirely on the microactuator type and configuration. In general, a piezoelectric actuator requires more force than an electrostatic actuator to produce the same amount of displacement, thus being characterized by high force and low displacement. An electrostatic comb or parallel plate driven actuator, on the other hand, is characterized by low force and high displacement. As a result, the flexure must provide enough rigidity to counteract the reaction forces of the microactuator. If the flexure is too compliant in both the in-plane and out-of-plane displacement directions, much of the slider displacement may be lost due to displacement/twisting of the flexure upon actuation. Also, since the reaction forces are transmitted from the microactuator to the flexure and then to the load beam, the reaction forces may excite undesired off-track displacement modes in the flexure.
Another problem that is encountered with such microactuator configurations, is the difficulty in transmittal of electrical signals to the slider. With the piezoelectric microactuators, the slider may be terminated with external, compliant flying or unsupported leads of the wireless flexure. However, terminating the slider in this manner could produce several problems or risks, including static attitude variation, assembly difficulty, stroke variation, and flyability, that is the ability of the head slider to fly above the disk, among others. With many of the other configurations, the microactuator may need to contain integral wiring to transmit the electrical signals from the flexure to the head slider. The requirement for integral wiring is especially important for electrostatic microactuators that generate small forces. For this situation, external flying or unsupported leads may not be used because the added stiffness of the leads may render the system motionless. The formation of integral wiring in an electrostatic microactuator would require very small electrical traces to be deposited and patterned on or off of thin silicon springs. One challenge for this situation is developing a multi-level metallization/plating process for fabricating the traces that connect the top bond pads of the microactuator to the bottom bond pads. Head suspension configurations that did not require direct electrical termination of the microactuator to the slider would be advantageous.
Another problem encountered with second-stage microactuation systems is shock robustness, especially in the piezoelectric configurations. In these configurations, the amount of shock able to be withstood is limited by the fracture limit of the piezoelectric material because much of the shock load passes through the piezoelectric element. Making the piezoelectric element thicker, wider or shorter will increase the shock robustness by increasing the stiffness of the element, but these changes will also result in a decrease in the amount of stroke provided by the element. Increases in shock robustness without losing stroke capability would be advantageous.